Electrodynamic pickup



Y 1950 J. DE BOER ET AL ELECTRODYNAMIC PICKUP Filed July 20, 1946 Jan De. Boevamofi Gevvit Schenkal INVENTORS Patented May 30, 1950 ELECTRODYNAMIC PICKUP Jan de Boer and Gerrit Schenkel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Gonn, as

trustee Application July 20, 1946, Serial No. 685,192 In the Netherlands July 9, 19 13 Section 1, Public Law 690, August 8, 1946 Patent expires July 9, 1963 9 Claims.

The invention relates to an electrodynamic pick-up for oscillations mechanically provided in grooves on a carrier, for example recorded sound vibrations, wherein the coil holder provided with a needle is suspended between two points in the direction of movement of the groove. It is customary in this case to mount the coil holder on the middle portion of the wire or strip between the two points of suspension.

If a pick-up of this type is utilized for the reproduction of a sound record in Berliner recording, wherein the width of the track, viewed in a direction perpendicular to the direction of movement, always remains constant, there arise difiiculties due to the fact that for the reproduction of the sound use is practically always made of needles having more or less rounded points. These difiiculties will be set out in detail with reference to Figure 1 of the accompanying drawmg.

This figure represents, on an enlarged scale, part of groove of a gramophone record, which groove has a constant depth. Since the width of the recording stylus used for providing this groove has always the same size in the direction perpendicular to the forward movement; this groove consequently also has in this direction at any point the same width or in other words the arrows in the figure are of the same size at A and at B. It follows therefrom that in a direction perpendicular to the wall the groove has an unequal width, for example, at C the arrow is smaller than at A or at B. It follows from the 'foregoing that in the case of large amplitudes a smaller track will thus be produced for larger sections thereof in general than in case of smaller amplitudes.

A gramophone needle of the above-mentioned shape must be so large that it exactly fills the groove at the points at which the latter is widest (of. S in the figure). In such case, however, the groove, which is narrower further on, can no longer contain the entire needle at T so that the latter is lifted up. The same eifect occurs, of course, if the gramophone record utilized is not exactly plane.

If the coil holder is secured to the wire or strip at a point intermediate between the two points of suspension, it has to overcome in its upward movement a rather appreciable force, viz. the tension on the wire or strip caused by the fact that the whole of the pick-up follows this movement. The result thereof is that the r cord and the needle are subject to fairly strong abrasion. Moreover, the quality of the reproduction is harmfully alfected.

The present invention has for its object greatly to reduce these harmful consequences of the upward movement of the pick-up. This is achieved by the fact that the point at which the coil holder is secured to the suspension wire or strip is located at unequal distances from the two points of suspension. The consequence thereof is that when the gramophone needle jumps up the whole of the pick-up does not follow this upward movement in the vertical direction but that chiefly only the coil holder performs a, rotary motion about a centre of rotation which is located on the side of the nearest point of suspension. The force which has to be overcome in this case is much smaller, which results in a reduced abrasion of needle and carrier and in a higher quality of reproduction.

A further improvement of this effect is obtained by taking the step known in itself wherein the axis of symmetry of the coil holder is chosen to occupy an ablique position with respect to the carrier. Thus, the distance through which the needle must jump up is reduced in the axial direction.

In order to avoid that during the reproduction the means of suspension of the coil holder enter into contact with the carrier, the coil holder is preferably mounted on the strip or wire in such manner that in the operating condition this wire or strip is parallel to the carrier. This offers the additional advantage that the moment of inertia of the coil holder with respect to the wire or strip is reduced, which is beneficial to the quality of the reproduction since the coil holder can oscillate more elastically.

The invention will be explained in detail, applied to one possible form of construction, with reference to Figures 2 and 3 of the accompanying drawing. These figures represent diagrammatically a plan-view and a side-view respec--. tively of a groove pick-up according to the invention.

A coil holder consisting, for example, of a cylindrical portion Ia and a conical portion lb, for example of aluminium, is secured to a strip 2 and at a location nearer to the point of suspension 3 than to the point of suspension 4. At these points the strip is secured with a certain tension to the portions 5 and 6 of the pick-up. The pole shoes of a magnet l surround the cylindrical portion of the coil holder, this magnet being omitted in Figure 3 for the sake of clearness. The coil is wound on the cylindrical portion I a of the coil holder, while the whole of the coil holder I is hollow for the purpose of saving weight. In Figure 2 the coil holder l is shown likewise for the sake of clearness, in a perpendicular position with respect to the strip. Figure 3 shows furthermore a needle 8 which bears on a carrier 9.

When the needle jumps up in the groove, it performs chiefly, both in the form of construction shown in Figure 2 and in Figure 3, a rotary motion in the direction of the arrow, for example, about a centre of rotation l8, owing to the fact that the short strip portion located 'jnear ,the point 10 has a greater rigidity than the longer remainder of this strip. Ihe movement is followed by the whole of the coil holder since the latter is constructed so as to form a rigid unit, the form of construction chosen being extremely suitable for this purpose.

In connection with the possibilities of construction the strip may at will either consist of one piece and pass through the cylindrical portion la, as shown in Figure 2, "or it may consist of two portions which are each secured to the edges of the cylindrical portion 1a.

What we claim is:

1. An electrodynamic pick-up for oscillations mechanicall provided in grooves on a movable carrier, said pick-up comprising a coil, a holder therefor, and a stylus beneath said coil at the foot of said holder; and resilient suspension means for said coil holder wholl supported between two points spaced at opposite sides of said coil holder in the direction of movement of the groove, said two points being at unequal distances from said coil holder.

2. A gramophone comprising a grooved carrier; means for moving said carrier; and an electrodynamic pick-up including a coil, a holder therefor. astylus at the foot of said holder to ride in said carrier groove; said groove having means to impart .a vertical component of motion to said stylus as said carrier is moved and resilient suspension means disposed parallel to the plane of said carrier and wholly supported between two points spaced at opposite sides of said coil holder in the direction of movement of said groove at said stylus, said two points being at unequal distances from said coil holder.

3. An electro-dynamic pick-up for oscillations mechanicall provided in grooves on a movable carrier, said pick-up comprising a coil, a holder therefor, said holder comprising a cylindrical portion and an adjoining conical portion, said groove having means to impart a vertical component of motion to said stylus as said carrier is moved, said cylindrical portion being provided with said coil, a needle secured to the apex of said conical portion, resilient suspension means connected to said coil holder and wholly supporting said holder between two points spaced at opposite sides of said holder in the direction of movement of the groove, said two points being at unequal distances from said coil holder.

4. A gramophone comprising a grooved carrier, means for moving said carrier, an electro-dynamic pick-up including a coil, a holder therefor, a stylus at the foot of said holder to ride in the groove of said carrier, resilient suspension means connected to said holder and disposed parallel to the plane of said carrier, said suspension means being supported between two points spaced in the direction of movement of said groove at said stylus, said two points being at unequal distances from said coil holder, the point at the longer distance from said coil holder being in the direction towards which said grooved carrier moves with respect to said coil holder.

5. A gramophone as claimed in claim 4 wherein said coil holder and said stylus are inclined towards said direction.

6. An electro-dynamic pick-up unit comprising a pair of spaced apart mountings, a coil holder located in the space between said mountings nearer to one of said mountings than to said other, a needle projecting from said coil holder, and resilient suspension means supporting said coil holder in position in said space, said resilient suspension means comprising a first elongate element section extending from said one of said mountings to said coil holder and a second e1ongate element section extending from said other of said mountings to said coil holder, said first section being substantially shorter than said second section, each of said sections being resilient in a plane substantially parallel to that of said coil holder.

7. An electro-dynamic pickup for oscillations mechanically provided in grooves on a movable carrier, said pick-up comprising a coil, a holder therefore, a stylus beneath said coil at the foot of said holder and resilient suspension means for said coil holder supported between two points spaced in the direction of movement of the groove, the axis of symmetr of said coil holder being in an oblique position with respect to said carrier.

8. An electro-dynamic pick-up for oscillations mechanically provi'ded'in 'grooveson a mechanical carrier, said pick-up comprising a coil, a holder therefore, a stylus beneath said coil at the foot of said holder and resilient suspension means for said 'coil holder supported between two points spaced in the direction of movement of the grooves, said two points being at unequal distances from said coil holder, said resilient suspension means comprising a strip mounted at an angle other than with respect to the axis of symmetry of said coil holder.

9. An electro-dynarnic pick--up unit comprising a pair of spaced apart mountings, a coil holder located in the space between said mountings nearer to one of said mountings than to said other, a needle projection from said 'coi-l holder, and resilient suspension means supporting said coil holder and positioned in said space, said resilient spacing means comprising a first elongate element section extending from said one of said mountings to said'coil holder and a second elongate section extending from said other of said other mountings to said coil holder, said first section being substantially shorter than said second section, said coil holder and .said needle projecting therefrom being supported in a position inclined to the plane of one of said sections and in a direction towards said second section.

JAN ns BOER.

GEBRIT SCHENKEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,689,339 Harrison Oct. 30, 1928 1,785,047 Quinby -1 Dec. 16, 1930 2,025,388 Henning l Dec. 24, 1935 2,161,489 Vieth et al. June 6, 1939 2,290,057 Lindenberg July 14, 1942 FOREIGN PATENTS Number Country Date 384,531 Great Britain Dec. 8, 1932 

